The invention relates to a linear motor comprising two motor sections which are movable relative to one another along a motor axis, a first motor section comprising a coil support carrying a system of coils whose turns are oriented transversely of the motor axis and a second motor section comprising a magnet support carrying at least one pair of magnets which, at least when viewed along the motor axis, are spaced at a distance from one another to form a gap and which are constructed to cooperate with the system of coils across an air gap.
The invention further relates to a positioning device comprising a frame, a positioning table and at least one linear motor.
Such a positioning device is known from U.S. Pat. No. 4,485,339. The prior-art device has a base plate carrying a first and a second coil, which are spaced from each other. The prior-art device further comprises a first magnet arranged in facing relationship with the first coil, a second magnet arranged in facing relationship with the second coil, and a linking member which magnetically links the two magnets and which has a supporting surface for an object to be positioned. The base plate, the magnets and the linking member together form a magnetic circuit and in conjunction with the coils they constitute a linear drive unit for the linking member.
The prior-art positioning device comprises a detection unit for detecting the position of the linking member and a control unit for controlling the magnitude and the direction of the electric current in the two coils in order to move the magnets and the linking member relative to the base plate along a linear path parallel to the aligned coil axes of the coils.
A drawback of the prior-art linear drive unit is that it can perform only a small travel in relation to the motor dimensions, in particular the dimension viewed along the coil axes, which requires a comparatively large and heavy construction of the positioning device for a predetermined travel. Another drawback of the prior-art linear motor is that in operation comparatively large energized parts of the coils do not effectively contribute to the generation of driving Lorentz forces, causing unnecessary power dissipation.